Definition
It seems simple. When you itch, you scratch. But itchy skin (pruritus) can have hundreds of possible causes. It may be the result of a rash or another itchy skin condition, such as psoriasis or dermatitis. Or itchy skin may be a symptom of an internal disease, such as liver disease or kidney failure. Though itchy, your skin may appear normal. Or it may be accompanied by redness, rough skin, bumps or blisters.
Symptoms
Itchy skin is an uncomfortable, irritating sensation that makes you want to scratch. It may occur in small areas, such as on an arm or leg. Or your whole body may feel itchy. Itchy skin can occur without any other noticeable changes on the skin. Or, it may be associated with:
Redness
Bumps, spots or blisters
Dry, cracked skin
Leathery or scaly texture to the skin
Sometimes itchy skin lasts a long time and becomes very intense. As you rub or scratch the area, it gets itchier. And the more it itches, the more you scratch. Breaking this itch-scratch cycle can be challenging.
Causes
Itchy skin that isn't accompanied by other obvious skin changes, such as a rash, is most often caused by dry skin (xerosis). Dry skin usually results from environmental factors that you can wholly or partially control. These include hot or cold weather with low humidity levels, long-term use of air conditioning or central heating, and washing or bathing too much.
Other conditions cause itchy skin as well. Skin disorders, internal diseases, allergies and drug reactions top the list.
Skin conditions and rashes. Many skin conditions cause itchy skin, including psoriasis, inflammation of the skin (dermatitis), scabies, lice, chickenpox and hives. In these cases, the itching usually affects specific areas and is accompanied by other signs, such as red, irritated skin or bumps and blisters.
Internal diseases. These include liver disease, malabsorption of wheat (celiac disease), kidney failure, iron deficiency anemia, thyroid problems and cancers, including leukemia and lymphoma. In these cases, the itching usually affects the whole body, rather than one specific area. The skin may look otherwise normal except for the scratched areas.
Irritation and allergic reactions. Wool, chemicals, soaps and other substances can irritate the skin and cause itching. Sometimes the substance causes an allergic reaction, such as in the case of poison ivy or cosmetics. Food allergies also may cause itchy skin reactions.
Drugs. Reactions to drugs, such as antibiotics, antifungal drugs or narcotic pain medications, can cause widespread rashes and itching.
Pregnancy. Some women experience itchy skin during pregnancy, especially on the abdomen, thighs, breasts and arms. Also, itchy skin conditions, such as dermatitis, can worsen during pregnancy.
Treatments and drugs
Once a cause is identified, treatments for itchy skin may include:
Medications. These include oral antihistamines for allergies or hives and corticosteroid creams for itching from skin inflammation.
Wet dressings. This involves applying medicated cream to affected areas and then covering these areas with damp cotton material that has been soaked in water or other solutions. The moisture in the wet dressings helps the skin absorb the medicated cream.
Treating the underlying disease. If an internal disease is found, whether it's kidney disease, iron deficiency or a thyroid problem, treating that disease often relieves the itch. Other itch-relief methods also may be recommended.
Light therapy (phototherapy). Phototherapy involves exposing your skin to certain wavelengths of ultraviolet light. Multiple sessions are usually scheduled until the itching is under control.
Although many types of itching respond well to treatment, itch relief may not be immediate. However, a number of creams and ointments are specifically designed to relieve itch. These include short-term use of topical anesthetics such as lidocaine or benzocaine and ointments and lotions such as menthol, camphor or calamine. Although these anti-itch products may immediately soothe your itch, treatment of the underlying cause is important for long-term relief.

mayoclinic.com/health/itchy-skin